Indicating bond tester



Oct. 21, 1930. c, VAWTER 1,779,347

INDICATING BOND TESTER Filed Jan. 7 1922 INVENTOR M 6" M M WW4 1 TTR/VE VS Patented Get. 21; 1 930 ciiaRLEs s; 'VAWTE R; on I HILADELPHIAJPENfisYLvANIA, ssIG oB, TO WESTON:

. "ELECT'RiGAL INSTRUMEN 0033011521011,os mwenx, E -messy, Aconrolm 1 TION OF New JER'SEY I D-mastit s. BoiIn TEsiERT' "Application filed January ail-322 ifserial;N ,52 7,711 ;fl;v a

' El e present invention relates to an indi-fl eating rail bond test'enand hasto do partied iariy with apparatus forindicating directly,

thei'esistan'ce'ofarail bond in tei'insfof a 5 fixe'dlength of rail. 7 f l I 'Due to the, fact that tracks on which rail bonds arebeing tested are usually in use and are carrying ci1r rent, it is impossible to measure the r'esista'iiceoi thebondbypassing 10 a direct current of known valuebetween the 7 ends of the-adj acent rails and measuring the corresponding values of the currents and of potential drop'across the bond; 'Gonsequent- 7 1y a testing instliiilneiit whose own measuring current is furnished byia battery or similar scarce cannot beused due to the fact thatthe current ali eady flowing in the rail would rendei: the readings out the instrument useless" Furthermore, the! magnitiide of the current; already flowing 1n the rail 1s nvarlablysum known so that it is impossible to compute the ieadings of the bon'dvby ineitely reading the potential dioplacross it. As a; result the.

testing ofsuchrail bond's'is commonly a'c'cOmT' plished" by comparing in some .manner the potential drop' acros's the bond with the po tentialfdrop' 'aloiiga fixedlen'gth of solid rail;

a method of testing curient carrying rail bonds it hasbeen proposed to take arfeading of the potential drop acifoss' the rail bond an d simultaneously take a "reading of f the vtiitage drop Whichoccurs over a givenlength of unbroken railtthe measurements being taken bytwo 'milhyoltmete 's 01; with the and of a:specialloyv resistancebridge. It is'eyi dent that from this data; giyingpthe ratio of potential drops over the raillcon-d and over a given length of unbroken raiL-th'atfby'sapiopef calculation the iresistancei of the" rail 4 bond can he expressedin feet ol -unbroken It is a p'iincipal object of the inyentionlto' provide an? indicating najilfbond testei 'jvhich may be easily and conyeniently applied ito the rail and will .indic at efdirectly electrical resistance of the rail bond expressed;

in ternisof. a given length ofl unbroken iail'.

j Itisaiixithei "object' to p oyidelan indicateing bond team- 0f theLabOVe type lwhich will giveaccurate readings ofithei'esistance of the railihond, even thoii'gh small currents afe curate indications regardless of-fluctuations .in theLciirrent traversing the rail. w It 1s also anjoh ect to prov de an-instrw;

inentof this type having a non-uniform scale,

the loweif portionpt the scale range being sensitive, so'th'at small resistances may be accurately read; anditheupper portion of the sufficient toproduce an accurate indication upon the ll'lStILUDGlltdf the resistance ofthe bond.

V ;I have illustrated a pi'eferredemhodiment flowing in therail, andwhich will give acof'm invention in th'e acconlpanyingdraw ings; in Which Fi giii e'l is a plan View of the indicatinginstruinent employed in my improved ma bondftes'ting apparatus; Fig.7 V

2 is a transverse sectionatviewi taken on 111152 2 o'fFig. 1 aris ng; 3 18a yiem'large diagrammatic; w n the i al nections en p'loyedin" my ;i p bondv The inmates1: aaaa t;em lo ed a connection with mygrail bond testing apparatusgji s an ohmmeteninstiumentot snb stan' tially' the same construction .as f the. instrument disclosed in'my. co-pending application,

Serial No. 527,705i-fild J an. 7, 1922, and comprises essentially a horseshoe magnet 1 provided with specially shaped pole pieces 2 for furnishing the magnetic field of lthe'insti-u inent, a specially shapedmagnetic core 3P0 sitione'd intermediate between the" poles of the magnet, and'aimovable element compris the coils 4 and 5 surrounding, respective- 1y, the' two. aimsB and 3F of the magnetic Core; The movable coil element also carries an indicating pointer 6 which "moves along a isnitable scale, 7 afiords an indication :ofthe various positionsassumed by the movable element. The pal-ts of the instiliinent niateiial foil shielding theinStrnmenhpatts fion l'strayfinagneticfields.

' are preferahly eniflosedfyiiithin abox orfcas- I iiig'B whichmay "be of iron 01' other magnetic As set forth in the above mentioned copending application, and also in Patent No. 1,426,619, granted to me on August 22, 1922, the character of the scale according to which the indicating pointer 6 will move is determined by the shape of the arms 3 and 3 of the magnetic core. That is, by properly shaping this core the instrument may have a scale of any desired type. In the'present instance it is to be noted that the arm 3 of the core continues with full cross section to its extremity, the inner and outer edges of the core being concentric circles whose center is coincident with the axis of rotation of the movable element. With this construction the air gap 9 occurring between the arm 3 of the core and the adjacent; pole piece of the magnet is uniform throughout its entire extent and consequently themagnetic flux traversing the gap will be substantially uniform throughout. On the other hand, the arm 3 of the core is materially shorter than the arm '3", and furthermore is abruptly tapered toward its end. This construction produces an air gap 10 betweenthe arm 3 and the adjacent pole piece which increases in width toward the tip of the arm 3*, and which will consequently be traversed by magnetic flux whose density decreases abruptly toward the tip of the arm. When the moving element of the instrument is in the position shown with the indicating pointer 6 near the lower end of the scale, thezcoil 4 lies in a portion of the air gap in which the magnetic flux density is relatively hi gh. Accordingly, a given change in current through the coil will cause a relatively large displacement'of the movable element about its axis, and the lower portion of the scale range will be correspondingly sensitive. As the moving element rotates farther in a clockwise direction. the'coil 4 moves into a magnetic field of decreased density due to the tapering of the core arm 3*, while coil 5 continues to move in a field of substantially constant density. In such position a given change in current through the coil 4 willproduce but a relatively slight displacement of the movable element, and the scale divisions along the .upper portion of the range must be placed correspondingly close together. This type of construction adapts the instrument for indicating accurately resistance magnitudes which cause the pointer 6 to come to reston the lowerportion of the scale range. I the resistance is relatively highit is not 'desiredto ascertain its exact value inasmuch'as it is obviously too high for economical use, and the bond must in any case be repaired. However, if the resistance of the bond is low it is desired to ascertain itsvalue accurately for use in computing the total resistance ofthe line. In such case the indicating pointer of theinstrument will come to rest along the lower portion of the scale range and the value of the resistance may be easily and accurately read directly from the instrument scale.

In manufacturing ohmmeter instruments, I have found that with apparently identical treatment the magnets are often somewhat different in strength and the distribution of magnetism along the metal of the magnet varies materially in different specimens. By means of the flux adjusting screw 11 these variations in magnet strength and distribution of magnetism may be compensated for and all instruments may be equipped with identical scales, adjusting screw 11 being used to bring the indicating pointer into proper registration with the scale markings after the instrument is completely assembled. If this screw be moved in close to the magnetic core 3 it is seen that the air gap at that point is materially reduced and consequently a larger amount of flux will pass from the pole piece to the core by way of the screw 11.

. In this sense the screw serves as a shunt path for a portion of the magnetic flux and affords a means for changing the character of the scale to a certain extent. It is further to be noted that this adjustment may be easily and conveniently made by merely removing the cover of the instrument and setting the screw 11to the desired position. When once properly adjusted, however, the screw 11 is normally left in its adjusted position without further attention.

A further advantage of the flux adjusting member 11 lies in the fact that it permits the parts of the instrument to be prepared and assembled without particular attention being paid to the accurate machining and mounting of the various parts. After the instrument is completely assembled and equipped with a scale 7 of predetermined character the movement of the pointer 6 may be caused to correspond to the markings. on the scale by merely applying the instrument to a known resistance and bringing the pointor to the correct position by adjusting the screw 11. I have indicated one of such. flux adjusting members, but it is evident that other such members may equally well be applied to the other arm of the horseshoe magnet or to the opposite ends of the pole pieces 2 without changing the character of the instrument. v

. In Fig. 3 I have illustrated the electrical connection of the indicating instrument together with a preferred method of making contact with the rail. The adjacent ends of the coils 4 and 5 are connected together and are attached to the binding post C provided onthe outside of the instrument casing. The other ends of the coils 4L and 5 are connected respectively to binding posts A and B of the instrument. These connections to the movable coil element may be made through contacts C, A and B, respectively, provided on i the. Vertical shaft of the .movable-ae-lemerits/as shown inFig; 2,.aand connectedlto the stationary parts. of the instrument through, light trailers o a and. 6, preferably of :gOlCl'OLI si1ver,twhi-ch exert substantially no torque on the-moving element .of the instrument.

"I preferably effect the connection-cf the indicating instrumentto the rail bY'QDJB'ELHS of ia con-tact bar 12. which maybeprovided with ahandle-13 for convenience in placing it ,uponztherail. .Near the ends of'ithe bar are placed-contacts 14A and MBcconnected, respectively, to the bindingposts A and B of the instrument, Adjacent one ofthese' contacts :is' provided. a third contact 14G con nectedto-bindi-ng post -C -and which may be conveniently mounted upon the lower, end of the'handle13, thehandle being mounted to 'sliide verticallyf in the bar, 12 so that. it m'ay be depressed into contact with the rail. A spring l-5isvsuppli-ed-to normally holdthe contact 140 out'E-of-engagement with the rail.

When the apparatus is applied to the testing of rail-bond the bindiig posts A, B 1 and C of the indicating instrument are connected to the contacts of the bar 12, as shown, and

the bar is placed upon the track so that the interval between the contacts. 14A and MC will span the rail ointv16.and the interval between contacts l l'C and 1413 will span a fixed length of unbroken rail. Immedi 1 ately upon placing the contact bar upon the track apotential difference will be created between contacts 14A and 1413 if there is current flowing in the rail, and such I potential difference will cause a current to ment is initially applied to the rail-if sufficient current be flowing in the rail for a measurement to be taken. Should the pointer not come immediately into this position when the instrument is applied to the rail the op-' erator will be in formed that there is not sufficient current fiowingin the rail to effect a test. V V The contact 14C may then be lowered by pressing the handle 13, in which case the coil 4: will be subjected to an electrical potential equal to thevoltage drop across the rail-joint due to the current flowingin the rail, andthe coil 5 will be subjected to a potential'equal' to the voltage drop along the-length of unbroken rail between contacts 14C. and 14B.

Accordingly a currentwill traverse coil 4 which is proportional to the resistance of the rail bond, and a current proportional to the Since the rail will traverse the coil 5. Inasmuch as the indication of the instrument is in proportion to the ratio of these two currents it isevid-ent that the scale may be conveniently calibrated to indicate the resistance of the rail bond in terms of 'a length of unbroken rail. For instance, the scale may be calibrated to indicate directly the number of feet of unbroken rail containing a resistanceequal to that of the rail bondunder test. In case only a small currentis present in the rail, such as is the case onste'am roads where the rail-carries only the current used for signalling purposes, it may bexdesirable to provide a few dry cells to furnish the. desired measuring current. The instrument 1s, however, adaptedto give accurate m'dicatlons when only a small-cur resistance of the fixed length of unbroken rentis present in the rail due tothe particular construction of the pole pieces, which are formed to surround asubstantialporti'on of f the periphery ofthe c011 and cause the greater part of the coil winding to be actively tray?" ersedbythe magnetiolines' of force.- Thus, a given current'through the 0011 will produce 7 atorque much greater than would be obtained if only Zone "side of the COll lZLY in the gap betweenl'the core and the magnet pole. V

. For the purpose of protectingthe instriinaientnincase of anexcessively high potential drop fiacross the Zrail bond and for the further purpose ofperrnitting resistances of higher valueto be indicated, upon the scale, I proyi'dea resistance coil 18. in circuit with the instrument preferably between the bin-d ingpost A andthe contact MA. This resist ito' ance may be of any desired Value; key-1 9 I, may convenientlybeprovided for the pur- .poseofshortcircuiting-the resistance 18 in:

case. it isidesired to ,subjectthe indicating instraunent directly to the potential of therrail. Inthe use of the instrument equipped with the resistance 18, the barf12 is placed in}. con v tact .with the :rail in r the usual manner, the key 19 beingleft inopen position. A swinging I ;of the pointer .in'to proximity with the r linelT on the scale .will indicate'that suflicient-current in flowing to effect atest, after Tin whichthe contact llGma-y belowered on to therail', In case an excessivepotential drop exists across. the bond theneedle of'the in 'strument will swing abruptly tofthe higher Values; on the scale,but will be protected by I the/resistance 18 ,which is in circuit with the coil 4.- If, however, the needle remains on the lower portion ofthe scale,-thekey 19 may be safely closed and a reading of the resistance oft-he bond taken in the ordinary manner. Inthe embodiment of the inyentlon described the current through the instrument is r produced solely by the potential drop along therail due to current flowing in the rail,{ rut it: is 1 evident that measurements be r;

talren iupon rails 'whichare; not carrying-current by'sup'plyingfan externalisource of elec tro-inotive force, such as a few dry cells and connecting them to the rail at points outside the fixed contacts 14A and 1413. The current from the dry cells will flow across the rail bond and through the length of solid rail spanned by the contacts 14-13 and 14C and will thus produce an indication on the instrument in the same manner as though a current were-flowing throughout the entire length of the track. It is further evident that other changes, such as the form of contact bar employed, the exact character of the instrument scale, the position of the balance point, and the like, may be varied without departing from the spirit of the invention. If desired. the arm 3 of the magnetic core need not be of constant thickness asfihas been described, but; may be reduced in thickness towards its end for the purpose of securing pro-per distribution of the flux in conjunction with the tapering in a lateral direction. Furthermore, it would be possible to secure a satisfactory scale even though both arms were tapered.

Further changes may be made within the full scope of the appended claim.

It is also to be noted that one or more adjusting screws 11 may be used as desired. I have illustrated only one such screw in the drawings, but the other pole of the magnet may be likewise provided with an adjusting screw 11, and, if desired, additional screws may be placed in proximity to the tips of the core arms 3 and 3 for the purpose of affording adjustments of great accuracy. In a rail bond tester of this type accurate readings are desired only along the lower part of the scale range, and I have found that satisfactory results are obtained by providing one adjusting screw 11 as shown, and bymeans of this single screw bringing the indicating pointer'ti into proper registration with some one point along the lower part of the scale range. For instance, a current may be sent through the two coils 4 and 5 in series, as would be the case in actual use when the middle contact 140 of the contact bar 12 is raised, and if the instrument is in correct adjustment the indicating pointer will lie between the heavy lines 17 marked on the scale. In case the pointer does not assume this position, it may readily be adjusted by merely changing the position of the screw 11. When accurate ly set for registration at this point on the scale the indicating pointer will coincide with all points throughout the lower part of the scale range with substantial accuracy.

I claim:

In a rail bond testing apparatus of the class described, the combination with a contact bar comprising a pair of fixed contacts and a third contact intermediate between the fixed contacts and adjacent one of them for spanning the rail bond being tested, a fixed length of unbroken rail lying between the intermediate contact and'the other of said fixed contacts, and means for adjusting said intermediate contact toward and away from the rail, of an indicating instrument having two serially connected coils, an indicating member actuated in response to the ratio of the currents traversing said coils, a scale asso ciated with said indicating member and having marked thereon a Zone within which said indicating member will come to rest when current sufficient to actuate said instrument traverses said coils in series, electrical connections between the outer ends of said coils and the respective fixed contacts, and an electrical connection between the junction of said coils and said third contact, whereby said coils may be first connected in series and subjected to the potential difference along the length of rail spanned by said fixed contacts, and may be subsequently subjected independently to the respective potential drops occurring between each fixed contact and the intermediate contact by the lowering of the movable contact into engagement with the rail. 7

In testimony whereof I affix my signature.

CHARLES E. V'AWTER. 

